1. Field of the Invention
The invention relates generally to emergency lighting systems normally operable from a mains power supply and configured to operate from an emergency power source on failure of mains power, the invention particularly relating to programmable self-test and/or self-diagnostic systems for emergency lighting fixtures and which are capable of manual or automatic performance of testing and diagnostic functions on the circuitry, power supply, charging system and lamping thereof.
2. Description of the Prior Art
Emergency lighting systems have become ubiquitous due to code requirements, power typically being provided to emergency lighting systems under normal operating conditions by mains power supplied both to a normal AC ballast for light generation and to an emergency ballast for maintaining a charge on a power supply typically carried by the emergency lighting system, the power supply usually taking the form of an internal battery. Loss of line voltage results in the switching of the emergency ballast to power the lamping of the emergency lighting system through the emergency power supply, power being typically provided to the lamping for operation of the emergency lighting system for a relatively short period of time. Since the emergency lighting system is effectively in stand-by mode during normal operation thereof, periodic testing of the system is desirable in order to ensure proper functioning during emergency conditions, that is, loss of mains power. Conventionally, emergency lighting systems are tested by the active intervention of building maintenance personnel by manual operation of a test switch to simulate a power outage and to monitor the operation of the emergency lighting system. Neglect of testing procedures often occurs and results in detection of the failure of the emergency lighting system only when an emergency situation arises. In relatively recent years, automatic self-test and/or diagnostic circuitry for emergency lighting systems has become available. In such circuitry, an internal control system such as a microprocessor automatically causes a number of different tests to be conducted in sequence, such tests including detection of lamp current flow, power transfer from charger to battery and battery voltage. Failure conditions are typically indicated in such circuitry through illumination of a visual indicator such as a light emitting diode to indicate that maintenance is required. Systems monitored at central locations would also produce an indication of test failure on a computer display terminal at a central monitoring location. Systems capable of automatic testing include the supervisory emergency lighting system disclosed by Balcom et al in U.S. Pat. No. 4,799,039, this patent also describing other emergency lighting systems having periodic testing and self-diagnostic capabilities. The supervisory system of Balcom et al continuously monitors selected parameters of an emergency lighting system and periodically tests the system under simulated full-load emergency conditions automatically. The Balcom et al system also includes a closed loop three-mode battery charging control circuit. Vosika et al, in U.S. Pat. No. 5,574,423, disclose a self-diagnostic circuit for an emergency lamp which includes a high-impedance circuit path connected in series with the lamp and including a visual indicator energized by battery current passing through the circuit path and lamp during standby mode operation. A second high impedance circuit path is connected in parallel with the lamp to energize a second visual indicator whenever proper electrical continuity does not exist through the lamp. In U.S. Pat. No. 5,666,029, McDonald automatically tests the emergency ballast of an emergency lighting system, testing functions being facilitated by providing the emergency ballast with a transistorized inverter cutoff unit.
While circuitry of the prior art provides improved testing and diagnosis of emergency lighting systems when compared to manual testing as has been standard in the art for many years, the art is improved by the present invention which provides a low power, low cost circuit board combining all functions of a self-test/self-diagnostic system with control of all diagnostic, charging and transfer functions through the use of software, a microprocessor so controlled not only monitoring operation of charger/transfer circuitry but also controlling the charger/transfer circuitry to enable alternate strategies for alleviation of a given failure. The present self-test and self-diagnostic circuitry is thus capable of optimal function at extraordinarily low cost, the present system thereby producing a valuable advance in the art.
The invention provides an emergency lighting fixture having both manual and automatic self-test/self-diagnostic capabilities and wherein all diagnostic, charging and transfer functions are controlled by a microprocessor operating with software instructions. Microprocessor control is accomplished without modification of standard charger, inverter and lamp topology such as are conventionally employed in emergency lighting systems now available in the marketplace. The present electronic self-test and/or self-diagnostic circuitry combines with an emergency lighting system to perform under manual or automatic control testing and diagnostic functions on the circuitry, power supply, charger and lamping of a fixture. The diagnostic circuitry of the invention not only monitors operation of charger/transfer circuitry but also controls such circuitry to enable implementation of alternate strategies for alleviation of a given failure. In an LED exit sign, for example, a two-stage inverter powers the light emitting diodes and is controlled by the microprocessor, the microprocessor being efficiently powered in inverter mode. Further, battery power supply to the microprocessor is controlled by the microprocessor and is discontinued after appropriate operation until primary power is restored. Configuration of the test and diagnostic system in an exit signage embodiment can occur through use of a two-wire serial link between modular elements of the system, allowing the system to be flexibly configured in a low power low cost circuit board, flexibility further being provided by separate treatment of lamping from charger and diagnostic electronics.
In the LED exit signage mode, the present diagnostic circuitry employs the two-stage inverter indicated herein as being controlled by a microprocessor to convert voltage from one or more cells to a higher voltage for driving a string of light emitting diodes such as form the lamping of the exit sign or the like, driving of the light emitting diodes being accomplished in a manner similar to that described in U.S. Pat. No. 5,739,639, the disclosure of which is incorporated hereinto by reference. An EEPROM memory is used in this embodiment of the present system to set factory determined configuration parameters, thereby allowing accurate calibration without the need to use unreliable and costly potentiometers and further providing a field diagnostic log containing information relating to testing and diagnostic history. The LED exit signage embodiment of the present system further utilizes all solid state transfer switches for switching between emergency charging and diagnostic modes, this embodiment of the invention not utilizing relays and therefore using less power with more reliability than prior systems so configured. Since the microprocessor used according to the invention controls its own power supply and turns itself off once battery voltage has reached a low voltage disconnect threshold, very low power is consumed once the required emergency discharge is complete, a further benefit which allows the system to be shipped in this first embodiment without disconnecting the battery. Emergency lighting fixtures configured according to this first embodiment of the invention therefore do not require connection of the battery on site during installation, thereby reducing on-site installation time and possible error. System flexibility in the LED exit sign embodiment of the invention is maximized through use of a two-wire serial data interface providing linkage between elements of the system which can be modular in nature and include optional circuit boards to allow optional features to be readily added to the lighting system. Software controlling the microprocessor of the invention in the LED exit sign embodiment of the invention, drives a low cost battery maintenance algorithm through use of a simple shunt circuit to reduce battery trickle charge current once the battery is charged, battery life thus being prolonged.
A second embodiment of the invention capable of self-test and/or self-diagnosis of emergency unit lighting fixtures is necessitated by differences in the-basic load and battery chemistries which exist between normally incandescent emergency unit fixtures and emergency exit signage illuminated by an array of light emitting diodes. While the first embodiment of the invention finds primary use with exit signage illuminated by light emitting diodes, the second embodiment of the invention is used in emergency unit fixtures wherein sealed lead-acid batteries are normally used to provide power for direct current lamps when AC mains power fails. Typical drain rates in the emergency mode of operation in such emergency unit fixtures range from three to thirty amps depending upon the number of direct current lamps operated within the unit fixture. By comparison, battery drain rates required from an efficient light emitting diode exit sign is less than approximately 650 milligrams. Accordingly, LED exit signs can be operated in the emergency mode by one or more NiCd batteries using a relatively simple current control charger. The use of lead-acid batteries in emergency unit fixtures requires use of a voltage-control charger in order to maintain the batteries properly in the normal, non-emergency mode of operation. The need for sealed lead-acid batteries in emergency unit fixtures is accompanied by the need for temperature compensation of charger output voltage in order to maximize battery life over a range of operating temperatures.
As a second consideration for the need for the two embodiments of the invention, a large difference exists in output mode requirements between emergency exit signage and unit emergency fixtures. In the situation involving an exit sign illuminated by light emitting diodes, in particular, the load is small enough to be driven with a small boost converter circuit having a battery-drain rate of less than 650 milliamps. In emergency unit fixtures utilizing incandescent lamping in the emergency mode, output load of greater than three amps necessitate use of a relatively simple relay transfer circuit for the output load. A further complication of the increased output load in emergency unit fixtures dictates that diagnostic circuitry for unit fixtures requires a more complicated current sense circuit as opposed to a relatively simple shunt element, that is, a resistor, as is used in the exit sign which is capable of functioning with the first embodiment of the circuitry of the invention. The self-diagnostic aspect of the second embodiment of the invention requires the diagnostic circuitry to measure both charge and discharge currents, such diagnostic circuitry therefore requiring a large dynamic range and being capable of measuring both positive and negative currents.
The second embodiment of the invention which is particularly useful with emergency unit fixtures having incandescent lamping is capable of operation without the use of an inverter. Further, the second embodiment of the invention does not provide a zero power consumption feature as occurs with the first embodiment of the invention, it being necessary to ship emergency unit fixtures so configured with the battery disconnected. Still further, the emergency unit fixtures having the second embodiment of the diagnostic circuitry forming a portion thereof utilizes a relay to connect direct current lamps to lead-acid batteries during emergency mode operation. A relay can preferably be used when the system is configured with lead-acid batteries. The battery-charging algorithm used in the emergency unit fixture is also more complex than the algorithm employed in the first embodiment of the invention which is used with LED emergency exit signage. The more complex algorithm is necessary due to the differing charger topology, the emergency unit fixtures requiring a voltage-control charger while the LED exit signs utilize a relatively current-control charger using a shunt regulation topology.
Accordingly, it is an object of the invention to provide electronic self-test and/or self-diagnostic systems particularly useful with emergency lighting fixtures, the systems performing testing and diagnostic functions on the circuitry, power supply, charger and lamping of a fixture either by manual or automatic initiation.
It is another object of the invention to provide diagnostic circuitry for emergency lighting systems which not only monitor operation of charger/transfer circuitry but also control the charger/transfer circuitry to enable implementation of alternate strategies for alleviation of a given failure.
It is a further object of the invention to provide self-test/self-diagnostic emergency lighting fixtures configured in a low power, low cost circuit board with control of all diagnostic, charging and transfer functions by means of software, the system including a standard charger, an inverter or relay and standard lamp topology.
It is a still further object of the invention to provide in a first embodiment of self-test/self-diagnostic emergency lighting fixtures an inverter controlled by a microprocessor and converting voltage from one or more cells to a higher voltage to drive lamping such as a light emitting diode array as in an exit sign, inverter operation being fully microprocessor controlled.
It is yet another object of the invention to provide in a second embodiment of self-test/self-diagnostic emergency lighting fixtures a relay transfer circuit controlled by a microprocessor and a voltage-controlled charger for operation of emergency unit fixtures utilizing incandescent lamping, operation of the fixtures being microprocessor controlled.
Further objects and advantages of the invention will become more readily apparent in light of the following detailed description of the preferred embodiments.